<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>圆角</title>
    <style>
      div{
        margin: 50px auto;
        width: 200px;
        height: 200px;
        background-color: orange;
        border-radius: 50px;
      }
    </style>
</head>
<body>
    <div></div>
</body>
</html>